The Copenhagen Diagnosis

More than three years have passed since the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC). Given that the AR5 isn’t due until 2014, it is perhaps appropriate that a group of scientists have released a more current summary of peer-reviewed scientific work on climate change, in the lead-up to the climate negotiations in Copenhagen next month.

The Copenhagen Diagnosis is intended as an interim evaluation. It was written by scientists from Germany, the US, Australia, Austria, Switzerland, the UK, and Canada (with the University of Victoria’s Andrew Weaver participating). Written by a comparatively small group of people, it doesn’t have the same level of authority as an IPCC report. Nonetheless, it seems appropriate that it be taken into consideration as states are considering what ought to be done about climate change. On methodology, the prefare to the report specifies that:

The science contained in the report is based on the most credible and significant peer-reviewed literature available at the time of publication. The authors primarily comprise previous IPCC lead authors familiar with the rigor and completeness required for a scientific assessment of this nature.

The report was published by the The University of New South Wales Climate Change Research Centre (CCRC) in Sydney.

Some of the key conclusions of the report include:

Global carbon dioxide emissions from fossil fuels in 2008 were nearly 40% higher than those in 1990. Even if global emission rates are stabilized at present-day levels, just 20 more years of emissions would give a 25% probability that warming exceeds 2°C.

Over the past 25 years temperatures have increased at a rate of 0.190C per decade, in every good agreement with predictions based on greenhouse gas increases. Even over the past ten years, despite a decrease in solar forcing, the trend continues to be one of warming. Natural, short- term fluctuations are occurring as usual but there have been no significant changes in the underlying warming trend.

A wide array of satellite and ice measurements now demonstrate beyond doubt that both the Greenland and Antarctic ice-sheets are losing mass at an increasing rate. Melting of glaciers and ice-caps in other parts of the world has also accelerated since 1990.

Summer-time melting of Arctic sea-ice has accelerated far beyond the expectations of climate models. This area of sea-ice melt during 2007-2009 was about 40% greater than the average prediction from IPCC AR4 climate models.

Satellites show great global average sea-level rise (3.4 mm/yr over the past 15 years) to be 80% above past IPCC predictions. This acceleration in sea-level rise is consistent with a doubling in contribution from melting of glaciers, ice caps and the Greenland and West-Antarctic ice-sheets.

By 2100, global sea-level is likely to rise at least twice as much as projected by Working Group 1 of the IPCC AR4, for unmitigated emissions it may well exceed 1 meter. The upper limit has been estimated as – 2 meters sea-level rise by 2100. Sea-level will continue to rise for centuries after global temperature have been stabilized and several meters of sea level rise must be expected over the next few centuries.

Several vulnerable elements in the climate system (e.g. continental ice-sheets. Amazon rainforest, West African monsoon and others) could be pushed towards abrupt or irreversible change if warming continues in a business-as-usual way throughout this century. The risk of transgressing critical thresholds (“tipping points”) increase strongly with ongoing climate change. Thus waiting for higher levels of scientific certainty could mean that some tipping points will be crossed before they are recognized.

If global warming is to be limited to a maximum of 2°C above pre-industrial values, global emissions need to peak between 2015 and 2020 and then decline rapidly. To stabilize climate, a decarbonized global society – with near-zero emissions of CO2 and other long-lived greenhouse gases – need to be reached well within this century. More specifically, the average annual per-capita emissions will have to shrink to well under 1 metric ton CO2 by 2050. This is 80-90% below the per-capita emissions in developed nations in 2000. (Emphasis mine)

In short, there are many good reasons to worry about the state of the climate system, as well as what will happen within it if humanity doesn’t begin effectively reducing our emissions. Hopefully, those messages will not be lost on the people negotiating in Copenhagen, even if the prospects for a comprehensive agreement are not looking terribly good right now.

The US and China have finally announced real numbers for their targets to reduce carbon emissions. Unfortunately these numbers, especially from the US, are far too weak. We need a strong agreement at Copenhagen, but this won’t get us there. In many ways, a weak agreement at Copenhagen could be even worse than no agreement, as it would lock in targets too small to make a significant difference.